HashAlgorithm Class
Represents the base class from which all implementations of cryptographic hash algorithms must derive.
System.Security.Cryptography.HashAlgorithm
System.Security.Cryptography.KeyedHashAlgorithm
System.Security.Cryptography.MD5
System.Security.Cryptography.RIPEMD160
System.Security.Cryptography.SHA1
System.Security.Cryptography.SHA256
System.Security.Cryptography.SHA384
System.Security.Cryptography.SHA512
Assembly: mscorlib (in mscorlib.dll)
The HashAlgorithm type exposes the following members.
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CanReuseTransform | Gets a value indicating whether the current transform can be reused. |
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CanTransformMultipleBlocks | When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed. |
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Hash | Gets the value of the computed hash code. |
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HashSize | Gets the size, in bits, of the computed hash code. |
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InputBlockSize | When overridden in a derived class, gets the input block size. |
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OutputBlockSize | When overridden in a derived class, gets the output block size. |
| Name | Description | |
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Clear | Releases all resources used by the HashAlgorithm class. |
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ComputeHash(Byte[]) | Computes the hash value for the specified byte array. |
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ComputeHash(Stream) | Computes the hash value for the specified Stream object. |
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ComputeHash(Byte[], Int32, Int32) | Computes the hash value for the specified region of the specified byte array. |
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Create() | Creates an instance of the default implementation of a hash algorithm. |
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Create(String) | Creates an instance of the specified implementation of a hash algorithm. |
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Dispose() | Releases all resources used by the current instance of the HashAlgorithm class. |
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Dispose(Boolean) | Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources. |
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Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
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Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
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GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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HashCore | When overridden in a derived class, routes data written to the object into the hash algorithm for computing the hash. |
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HashFinal | When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic stream object. |
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Initialize | Initializes an implementation of the HashAlgorithm class. |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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ToString | Returns a string that represents the current object. (Inherited from Object.) |
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TransformBlock | Computes the hash value for the specified region of the input byte array and copies the specified region of the input byte array to the specified region of the output byte array. |
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TransformFinalBlock | Computes the hash value for the specified region of the specified byte array. |
| Name | Description | |
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HashSizeValue | Represents the size, in bits, of the computed hash code. |
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HashValue | Represents the value of the computed hash code. |
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State | Represents the state of the hash computation. |
Hash functions are fundamental to modern cryptography. These functions map binary strings of an arbitrary length to small binary strings of a fixed length, known as hash values. A cryptographic hash function has the property that it is computationally infeasible to find two distinct inputs that hash to the same value. Hash functions are commonly used with digital signatures and for data integrity.
The hash is used as a unique value of fixed size representing a large amount of data. Hashes of two sets of data should match if the corresponding data also matches. Small changes to the data result in large unpredictable changes in the hash.
Notes to Inheritors
When you inherit from the HashAlgorithm class, you must override the following members: HashCore and HashFinal.
The following code example computes the SHA1CryptoServiceProvider hash for an array. This example assumes that there is a predefined byte array dataArray[]. SHA1CryptoServiceProvider is a derived class of HashAlgorithm.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Imports System.Security.Cryptography
Imports System.IO
Public Class FileChecksum
Private Const BUF_SIZE As Integer = 65536
''' <summary>
''' Returns the file integrity checksum hash, otherwise an empty string.
''' </summary>
Public Shared Function IntegrityCheck(ByVal filePath As String) As String
Dim dataBuffer(BUF_SIZE - 1) As Byte
Dim dataBufferDummy(BUF_SIZE - 1) As Byte
Dim dataBytesRead As Integer = 0
Dim hashResult As String = String.Empty
Dim hashAlg As HashAlgorithm = Nothing
Dim fs As FileStream = Nothing
Try
hashAlg = New MD5CryptoServiceProvider ' or New SHA1CryptoServiceProvider
fs = New FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None, BUF_SIZE)
Do
dataBytesRead = fs.Read(dataBuffer, 0, BUF_SIZE)
hashAlg.TransformBlock(dataBuffer, 0, dataBytesRead, dataBufferDummy, 0)
Loop Until dataBytesRead = 0
hashAlg.TransformFinalBlock(dataBuffer, 0, 0)
hashResult = BitConverter.ToString(hashAlg.Hash).Replace("-", "").ToLower
Catch ex As IOException
MsgBox(ex.Message, MsgBoxStyle.Critical, "IntegrityCheck")
Catch ex As UnauthorizedAccessException
MsgBox(ex.Message, MsgBoxStyle.Critical, "IntegrityCheck")
Finally
If Not fs Is Nothing Then
fs.Close()
fs.Dispose()
fs = Nothing
End If
If Not hashAlg Is Nothing Then
hashAlg.Clear() 'Dispose()
hashAlg = Nothing
End If
End Try
Return hashResult
End Function
End Class
- 7/14/2010
- eriklitze
